Apparatus for Monitoring Ion Implantation

ABSTRACT

An apparatus for monitoring an ion distribution of a wafer comprises a first sensor and a sensor. The first sensor, the second sensor and the wafer are placed in an effective range of a uniform ion implantation current profile. A controller determines the ion dose of each region of the wafer based upon the detected signal from the first sensor and the second sensor. In addition, the controller adjusts the scanning frequency of an ion beam or the movement speed of the wafer to achieve a uniform ion distribution on the wafer.

BACKGROUND

Since the invention of the integrated circuit, the semiconductorindustry has experienced rapid growth due to improvements in theintegration density of a variety of electronic components (e.g.,transistors, diodes, resistors, capacitors, etc.). This improvement inintegration density has come from shrinking the semiconductor processnode (e.g., shrink the process node towards the sub-20 nm node). As thedemand for miniaturization continues, the further shrinking of theprocess node may increase the complexity of fabricating integratedcircuits.

As semiconductor technologies evolve, semiconductor fabricationprocesses have become more sophisticated and hence require complexequipment and fixtures. In the semiconductor process, integratedcircuits are fabricated on a semiconductor wafer. The semiconductorwafer goes through many processing steps before a plurality ofintegrated circuits are separated by cutting the semiconductor wafer.The processing steps may include lithography, etching, doping anddepositing different materials.

Ion implantation is a processing technique for doping different atoms ormolecules into a wafer. By employing ion implantation, the majoritycharge carrier may be altered so as to produce regions in the waferhaving different types and levels of conductivity. In an ion implanter,an ion generator may generate an ion beam and direct the ion beamtowards the target wafer. In accordance with the cross section of ionbeams, ion implantation processes may be divided into two categories,namely a ribbon beam with a rectangular cross section and a spot beamwith a circular cross section.

Furthermore, in order to achieve a uniform ion distribution on thetarget wafer, either the wafer to be implanted or the ion beam isscanned. In accordance with the scanning pattern, ion implantationprocesses may be divided into two categories, namely a one-dimensional(1-D) ion implantation scan or a two-dimensional (2-D) ion implantationscan. In addition, a variety of ion implantation monitoring systems maybe employed to characterize ion beams before an ion implantation processoccurs. However, an unexpected fluctuation in the ion beams may cause anon-uniform ion distribution in the target wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a schematic diagram of an ion implantation system inaccordance with an embodiment;

FIG. 2 illustrates a top view of a ring-shaped beam profiler inaccordance with an embodiment;

FIG. 3 illustrates an effective range for placing ion plantation sensorsin accordance with an embodiment; and

FIG. 4 illustrates an embodiment method for monitoring ion implantationinvolving a one dimensional (1-D) mechanical scan and a two dimensional(2-D) mechanical scan in accordance with an embodiment.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the variousembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to preferredembodiments in a specific context, an apparatus for monitoring theuniformity of an ion implantation process. The invention may also beapplied, however, to a variety of ion implantation processes anddevices, such as high energy ion implanters, high current ionimplanters, medium current implanters and the like.

Referring initially to FIG. 1, a schematic diagram of an ionimplantation system is illustrated in accordance with an embodiment. Theion implantation system 100 comprises an ion beam generator 102, an ionbeam 104, a wafer 106 and an apparatus for monitoring an ionimplantation process. The ion implantation monitoring apparatus furthercomprises a ring-shaped beam profiler 108, a plurality of sensors 112and 114, a plurality of current meters 116 and 118 and a controller 120.As shown in FIG. 1, the ion beam generator 102 generates the ion beam104 and directs the ion beam 104 towards the wafer 106 as well as thesensors 112 and 114. The controller 120 receives detected iondistribution information and compensates the current of ion beam 104 byeither adjusting a scanning frequency of the ion beam 104 or adjustingthe movement speed of the wafer 106 relative to the ion beam 104.

The wafer 106 may be made of silicon or other semiconductor materialssuch as silicon germanium. The wafer 106 may go through many processingsteps such as lithography, etching, doping before a completed die isformed. During a doping process, the wafer 106 may be placed on a waferholder 130 for an ion implantation process. The quality of the completeddie may depend largely on the uniformity of ions embedded in the wafer106. For example, an uneven distribution of ions in the wafer 106 maycause a poor drive current uniformity (IDU) or threshold voltageuniformity (VTU) in transistors of the wafer 106.

In order to achieve a uniform ion distribution during an ionimplantation process, the ring-shaped beam profiler 108 is employed toaccommodate a plurality of sensors 112 and 114. In accordance with anembodiment, the ring-shaped beam profiler 108 is formed of graphite. Asshown in FIG. 1, the ring-shaped beam profiler 108 and the sensors 112and 114 are placed adjacent to the wafer 106. As a result, the sensors112 and 114 may receive the same ions as the wafer 106 during an ionimplantation process. It should be noted that while FIG. 1 shows boththe sensors 112 and 114 are mounted on the ring-shaped beam profiler108, the sensors 112 and 114 can be embedded in the ring-shaped beamprofiler 108.

FIG. 1 further illustrates the ion beam generator 102. The ion beamgenerator 102 may comprise a variety of components (e.g., ion separationand ion acceleration devices) to generate the ion beam 104 and directthe ion beam 104 toward the wafer 106. The detailed configuration of theion beam generator 102 is not illustrated herein so as to avoidunnecessary dilution of the innovative aspects of the variousembodiments. The ion beam 104 may be a spot beam, which has a circularcross section. Alternatively, the ion beam 104 may be a ribbon beam,which has a rectangular cross section. An ion beam (e.g., ion beam 104)may be of a smaller cross section than the diameter of the wafer 106. Inorder to achieve a uniform ion distribution on the wafer 106, eitherscanning an ion beam or moving a wafer relative to an ion beam isemployed to increase the wafer area to be implanted evenly.

In accordance with an embodiment, the ion beam 104 may have aGaussian-type non-uniform beam current distribution. More particularly,the ion beam 104 may have a bell shape in the middle and two long tailson both sides. A scan path is formed by scanning the ion beam 104 along±Y directions shown in FIG. 1. Along the scan path, the bell shapeportion and the long tail portion of the ion beam 104 are averaged toform a uniform beam current distribution. The uniform beam currentdistribution may be commonly referred to as an ion beam current profile.

In accordance with an embodiment, a plurality of sensors 112 and 114 arelocated within the uniform ion beam current distribution. As such, thesensors 112 and 114 may receive the same number of ion particles as thewafer regions similar in size. Furthermore, while FIG. 1 shows twosensors 112 and 114, additional sensors may be placed on the ring-shapedbeam profiler 108 so that the ion particle density of each sub-regionsof the wafer 106 can be better estimated. The sensed signals from thesensors are sent to a plurality of current meters (e.g., current meter116) coupled to the sensors respectively.

In accordance with an embodiment, a Faraday detector such as a Faradaycup may be implemented to achieve the function of sensing ion particlesfrom the ion beam 104 and converting the number of sensed ion particlesinto a current value. In other words, the sensor (e.g., sensor 114) andthe current meter (e.g., current meter 116) may be replaced by a Faradaycup. The operation details of Faraday cup are well known in the art, andhence are not discussed in further detail.

The current signals from the current meter 116 and the current meter 118are sent to a controller 120. The controller 120 may be amicroprocessor, a computer and/or the like. Based upon the currentsignals, the controller 120 calculates the ion distribution of eachregion of the wafer 106. Furthermore, by employing a feedback algorithm,the controller 120 may adjust either the scanning frequency of the ionbeam 104, the movement speed of the wafer 106 or a combination thereof.For example, when the controller 120 determines that the number of ionparticles received by a region of the wafer 106 is low, the controller120 may send signals to slow down the scanning frequency of the ion beam104 when the region is passing through the ion beam 104. Alternatively,the controller 120 may send signals to slow down the movement speed ofthe wafer 106 from the time the region starts to receive ion particlesto the time the region moves away from the ion beam 104. An advantageousfeature of having a plurality of sensors placed adjacent to the wafer106 is that the ion density of each region of the wafer 106 can bebetter estimated so that a uniform ion implantation process can beachieved by employing a feedback mechanism to adjust either the scanningfrequency of the ion beam 104 or the movement speed of the wafer 106.

FIG. 2 illustrates a top view of a ring-shaped beam profiler inaccordance with an embodiment. The ring-shaped beam profiler 108 may bea donut-shaped object. The inner diameter of the ring-shaped beamprofiler 108 may be 300 mm or 450 mm in response to wafer sizevariations. The outer diameter of the ring-shaped beam profiler 108 maybe 20 mm more than the inner diameter (not to scale for betterillustrating the ring-shaped beam profiler 108). On the ring-shaped beamprofiler 108, there may be a plurality of sensors (e.g., sensor 112).Each sensor is coupled to a current meter (not shown). In accordancewith an embodiment, the sensors (e.g., sensor 112) are formed ofgraphite. In order to have the sensors detecting ions, there may be aplurality of graphite regions on the ring-shaped beam profiler 108. Thegraphite regions may be formed on top of the ring-shaped beam profiler108. Alternatively, the graphite regions may be embedded in thering-shaped beam profiler 108. It should be noted that in FIG. 2 thegraphite regions are substantially rectangular in shape. It is withinthe scope and spirit of the invention for the graphite regions tocomprise other shapes, such as, but no limited to oval, square, circularand the like.

FIG. 3 illustrates an effective range for placing ion plantation sensorsin accordance with an embodiment. An embodiment ion implantationmonitoring apparatus including a ring-shaped beam profiler is shownabove with respect to FIG. 2. However, the implementation of the ionimplantation monitoring apparatus is not limited to a donut-shaped ring.Instead, a variety of alternatives can be used to accurately estimatethe ion implantation distribution on the wafer 106. For example, whenthe ion beam 104 scans along ±X directions shown in FIG. 3, an effectivebeam current range or region is generated as indicated by a dashed lineA and a dashed line B. Within the effective range or region, by scanningthe ion beam 104, the ion beam generator (not shown) generates a beamcurrent profile, which is uniform between the dashed line A and thedashed line B. As such, the sensors as well as the ring-shaped beamprofiler 108 can be any shape as long as they are located within theeffective range of the ion beam 104. In addition, the sensors and thering-shaped beam profiler may be attached to the wafer or the wafersupport apparatus (e.g., a wafer holder). As a result, the sensors canshare the same movement as the wafer 106.

FIG. 4 illustrates an embodiment method for monitoring ion implantationinvolving a one dimensional (1-D) mechanical scan and a two dimensional(2-D) mechanical scan in accordance with an embodiment. A first 1-Dmechanical scan 402 shows that a spot beam 422 moves back and forthbetween two endpoints. As a result, a uniform ion plantation currentprofile is generated along the scanning path between the two endpoints.At the same time, the wafer 106 as well as the ring-shaped beam profiler108 may move across the scanning path as indicated by the double-headedarrow. The relative movement of the wafer 106 helps to produce a uniformion dose on each region of the wafer 106.

Furthermore, because the ring-shaped beam profiler 108 movessimultaneously with the wafer 106 and the ring-shaped beam profiler 108is located within the effective range of the uniform ion implantationcurrent file, the detected ion dose on the sensors (not shown) of thering-shaped beam profiler may reflect the ion dose of the wafer 106. Byemploying additional sensors, the additional sensors may help to providea better resolution of the ion dose of each region of the wafer 106.Furthermore, additional sensors may help to determine the angle ofincidence of the ion beam 104.

FIG. 4 further illustrates a ring-shaped beam profiler 108 applicable toa ribbon beam 424 of a 1-D mechanical scan. Implementing an ionimplantation process using a ribbon beam is well known in the art, andhence is not discussed in detail to avoid unnecessary repetition.Similar to the ring-shaped beam profiler 108 described above withrespect 402, a second 1-D mechanical scan 404 shows the ring-shaped beamprofiler 108 is located within the effective range of a uniform beamcurrent profile. In addition, the ring-shaped beam profiler 108 movessimultaneously with the wafer 106. As such, by employing a plurality ofsensors on the ring-shaped beam profiler 108, the sensors can detect theion dose of the wafer 106.

FIG. 4 further illustrates a ring-shaped beam profiler 108 applicable toa spot beam 426 of a 2-D mechanical scan. Implementing an ionimplantation process using a 2-D mechanical scan is well known in theart, and hence is not discussed in detail to avoid unnecessaryrepetition. The double-headed arrow 416 indicates the movement path ofthe wafer 106 as well as the ring-shaped beam profiler 108. In otherwords, the wafer as well as the ring-shaped beam profiler 108 may passthe stationary ion beam multiple times along the horizontal direction.At the same time, the wafer 106 as well as the ring-shaped beam profiler108 may move vertically in a small step. The 2-D movement of the wafer106 may result in uniform exposure of the ion beam. As such, byemploying a plurality of sensors on the ring-shaped beam profiler 108,the sensors can detect the ion dose of the wafer 106.

Although embodiments of the present invention and its advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the invention as defined by the appended claims.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. An apparatus comprising: a wafer holderconfigured to support a wafer; a first sensor configured to movesimultaneously with the wafer holder, wherein the first sensor and thewafer holder are located within an effective region of a uniform ionimplantation current profile; and a first current meter coupled to thefirst sensor receiving a first sensed signal from the first sensor. 2.The apparatus of claim 1, further comprising: a second sensor configuredto move simultaneously with the wafer holder, wherein the second sensoris located within the effective region of the uniform ion implantationcurrent profile; and a second current meter coupled to the second sensorreceiving a second sensed signal from the second sensor.
 3. Theapparatus of claim 2, further comprising a ring-shaped beam profilerwherein: the ring-shaped beam profiler is placed adjacent to the waferon the wafer holder; the first sensor is placed on the ring-shaped beamprofiler; and the second sensor is placed on the ring-shaped beamprofiler.
 4. The apparatus of claim 1, further comprising a controllerconfigured to generate a 1-D mechanical scan of a spot ion beamgenerating the uniform ion implantation current profile.
 5. Theapparatus of claim 1, further comprising a controller configured togenerate a 1-D mechanical scan of a ribbon ion beam generating theuniform ion implantation current profile.
 6. The apparatus of claim 1,further comprising a controller configured to generate a 2-D mechanicalscan of a spot ion beam generating the uniform ion implantation currentprofile.
 7. The apparatus of claim 1, wherein the first sensor is madeof graphite.
 8. The apparatus of claim 1, further comprising: a firstFaraday cup detecting ion particles, wherein the first Faraday cup isplaced adjacent to the wafer on the wafer holder; and a second Faradaycup detecting the ion particles, wherein the second Faraday cup andfirst Faraday cup are symmetrical relative to the wafer.
 9. A systemcomprising: an ion beam generator; an ion implantation monitoringapparatus comprising: a wafer holder configured to support a wafer; afirst sensor configured to move simultaneously with the wafer holder,wherein the first sensor and the wafer holder are located within aneffective region of a uniform ion implantation current profile; and afirst current meter coupled to the first sensor receiving a first sensedsignal from the first sensor; and a controller coupled to the firstcurrent meter.
 10. The system of claim 9, further comprising: a secondsensor configured to move simultaneously with the wafer holder, whereinthe second sensor is located within the effective region of the uniformion implantation current profile; and a second current meter coupled tothe second sensor receiving a second sensed signal from the secondsensor.
 11. The system of claim 10, wherein the controller is configuredto: adjust a scanning frequency of an ion beam based upon the firstsensed signal and the second sensed signal; and adjust a movement speedof the wafer holder based upon the first sensed signal and the secondsensed signal.
 12. The system of claim 9, wherein the ion beam generatorgenerates a spot ion beam employing a 1-D mechanical scan to form theuniform ion implantation current profile.
 13. The system of claim 9,wherein the ion beam generator generates a ribbon ion beam employing a1-D mechanical scan to form the uniform ion implantation currentprofile.
 14. The system of claim 9, wherein the wafer holder and the ionbeam generator form a 2-D mechanical scan to generate the uniform ionimplantation current profile.
 15. The system of claim 9, furthercomprising a ring-shaped beam profiler wherein the ring-shaped beamprofiler is placed adjacent to the wafer on the wafer holder; and aplurality of sensors made of graphite are placed on the ring-shaped beamprofiler.
 16. A method comprising: generating a uniform ion implantationcurrent profile from an ion beam; placing a first sensor within aneffective range of the uniform ion implantation current profile; andestimating a first ion dose based upon a first detected signal from thefirst sensor.
 17. The method of claim 16, further comprising:determining an ion dose distribution by a controller; and adjusting ascanning frequency of the ion beam based upon the ion dose distribution.18. The method of claim 16, further comprising: determining an ion dosedistribution by a controller; and adjusting a movement speed of a waferholder based upon the ion dose distribution.
 19. The method of claim 16,further comprising: placing a ring-shaped beam profiler on a waferholder, wherein the ring-shaped beam profiler has an inner diameterequal to a diameter of a wafer; placing at least a sensor on thering-shaped beam profiler; determining an ion dose of a region of thewafer based upon a signal from the sensor; and adjusting a scanningfrequency of the ion beam.
 20. The method of claim 16, furthercomprising: placing a plurality of Faraday cups within the uniform ionimplantation current profile; and determining an ion dose based upondetected signal from the plurality of Faraday cups.